As a thermocouple using platinum, for example, an R thermocouple using a wire, which is formed from a platinum-rhodium alloy (rhodium 13%), as a positive electrode (positive pole) and a wire, which is formed from pure platinum, as a negative electrode and an S thermocouple using a wire, which is formed from a platinum-rhodium alloy (rhodium 10%), as a positive electrode and a wire, which is formed from pure platinum, as a negative electrode are mentioned.
When the wire formed from a platinum-rhodium alloy and the wire formed from pure platinum are compared with each other, since in the case of the pure platinum wire, creep strength is low and rupture occurs at an early stage, there is a problem in that the lifetime of the thermocouple is determined depending on rupture of the pure platinum wire.
In this regard, there is proposed a technique in which a Pt purity of a platinum wire is controlled to 5 N or more and zirconium oxide is dispersed in the wire so that occurrence of rupture is suppressed (for example, see Patent Literature 1).